One method of treating spinal disorders involves anchoring a screw or a hook to a patient's vertebrae. The screws or hooks are fixed along a spinal rod to position or immobilize the vertebrae with respect to one another. The screws or hooks commonly have heads with channels in which the spinal rod is inserted and subsequently clamped in place by a set screw, fastener, or locking cap. The spinal rod may be shaped to maintain the vertebrae in an orientation to correct the spinal disorder (e.g., to straighten a spine having abnormal curvature). Additionally or alternatively, the screws or hooks may be spaced along the rods to compress or distract adjacent vertebrae.
It is not uncommon for the spinal rod to require adjustment and/or removal during the course of treatment. Adjustment or removal of the spinal rod requires the locking cap be removed or loosened from the bone screw head. Unfortunately, surgeons often encounter considerable difficulty when removing or adjusting a locking cap due to sticking or “locking” of the cap within the bone screw. Because the bone screw and locking cap are subjected to prolonged immersion in bodily fluids, the threads of these components can become “locked” together due to the shear-thinning properties of blood coupled with blood's natural congealing process when exposed to air. The threads can also become locked together due to the cold welding effect of the thread surfaces of the locking cap and the screw head.
One current method of addressing the thread locking of the screw head and locking cap include the cyclic application of a tightening and loosening torque using a torque-limiting handle. This, and other methods for “unlocking” a locking cap, frequently result in the application of a torque in excess of the locking cap's design limits causing fracture of the locking cap and the potential for non-implantable grade stainless steel to become buried within the bone screw/implant. Therefore, a need exists for a device that provides for the removal of a “locked” locking cap thereby reducing procedure completion time and risk to the patient.